1. Field of the Invention
The present invention relates to an electric joystick mechanism for an ophthalmic apparatus, which moves an ophthalmic examination unit horizontally.
2. Description of Related Art
In recent years, in an ophthalmic apparatus which requires alignment with respect to an examinee's eye (e.g., an auto refractometer, a fundus camera), such an apparatus that electrically detects manipulation of a joystick and a trackball by an examiner and electrically drives an ophthalmic examination unit having a measurement optical system and other elements based on a result of the detection is proposed (see Japanese Patent Application Unexamined Publication No. 2002-369799).
In the apparatus disclosed in Japanese Patent Application Unexamined Publication No. 2002-369799, driving and control of the examination unit is divided into positional control and velocity control in accordance with a tilting angle of the joystick. In addition, a technique of controlling the examination unit so that movement velocity increases with an increase of the tilting angle in a range of the tilting angle of the joystick (e.g., 20 degrees to 35 degrees) which is beyond a predetermined angle.
The joystick mechanism disclosed in Japanese Patent Application Unexamined Publication No. 2002-369799 is provided with a first rotation shaft which rotates together with tilting movement of the joystick in a back/forth direction, a first potentiometer which detects a rotation angle of the first rotation shaft, a second rotation shaft which rotates together with tilting movement of the joystick in a right/left direction and a second potentiometer which detects a rotation angle of the second rotation shaft, and is arranged to electrically detect the manipulation of the joystick by the examiner by converting the tilting movement of the joystick into rotation movement of the rotation shafts in the back/forth direction and in the right/left direction.
The above-described electric joystick mechanism is desired to reflect an intention of the examiner and to have high operability. However, in the apparatus disclosed in Japanese Patent Application Unexamined Publication No. 2002-369799, fine angle adjustment of the joystick is difficult to be performed, and the examination unit could unintentionally move at a speed which is against the examiner's intention when the velocity control is performed in the range of the tilting angle of the joystick which is beyond the predetermined angle. In addition, it is necessary to largely tilt (e.g., at 35 degrees) the joystick in order to move the examination unit quickly, which takes time and effort for the examiner. In addition, the joystick mechanism disclosed in Japanese Patent Application Unexamined Publication No. 2002-369799 is complicated in structure as a whole because the rotation shafts which are different in shape need to be prepared (in the vicinities of connections with the joystick) in order to convert the tilting movement of the joystick into the rotation movement of the rotation shafts in the back/forth direction and in the right/left direction.